The invention relates to glass compositions of the silica-soda-lime type, intended for the production of flat glasses. Although the invention is not limited to such an application, it will be more particularly described with reference to applications for motor vehicles, especially side windows.
Glazing intended for the motor-vehicle industry is subject to various requirements, especially with regard to its optical properties; these requirements are governed by regulations, for example with regard to light transmission of a windscreen or else with respect to concern for the comfort of the user, for example with regard to energy transmission, or indeed with respect to concern for the aesthetic appearance, especially with regard to colour.
With regard to side windows, the requirements in terms of light transmission and of energy transmission may be less strict than in the case of windscreens. On the other hand, motor-vehicle manufacturers impose requirements in terms of colour and more specifically with regard to the dominant wavelength.
The colour of glazing is obtained by the addition of colouring agents in the batch materials intended to be melted in order to produce the glass matrix. These colouring agents are, for example, iron, selenium, nickel, chromium, cobalt, tungsten, vanadium, cerium, etc.
Some of these oxides are costly and for this reason are avoided or used in very small amounts; other agents are deemed to be very polluting and require filtration plants which during melting are between 70 and 85%, thus coming into this latter category and deemed to be very polluting. Furthermore, it is very difficult to control the chemistry because of the existence of several oxidation states of selenium in a glass.
Moreover, to produce grey glass, it is normal practice to use selenium. Melting plants are therefore provided with filtration systems specific to this element in order to prevent polluting of the atmosphere, making it expensive to produce these compositions.
The inventors were thus given the task of designing grey glass compositions of the silica-soda-lime type which have an overall light transmission under illuminant A (TLA) of greater than 15% for a thickness of 4.85 mm, the production, and especially the melting, of which is less expensive than the solutions already known, and the risks of pollution, especially due to selenium, being eliminated.
The invention relates to a grey glass composition of the silica-soda-lime type having an overall light transmission under illuminant A (TLA) of greater than 15% for a thickness of 4.85 mm and having the colouring agents given below within the following weight limits:
where Fe2O3 is the total iron.
The inventors have thus been able to determine novel grey glass compositions which may be produced relatively inexpensively and the selenium pollution risk of which is completely eliminated. This is because the selenium values according to the invention correspond to values of impurities that can be provided by certain batch materials. The manufacturing costs are thus reduced since filtration plants, such as those described above, which are often expensive, are unnecessary according to the invention.
The NiO content is preferably greater than 700 ppm and more preferably between 850 and 880 ppm.
According to a preferred embodiment of the invention, the overall energy transmission TE is less than 37%, preferably less than 30% and even more preferably less than 25% for a thickness of 4.85 mm. Such requirements correspond in particular to those required for motor-vehicle applications in order to ensure the comfort of persons in the passenger compartment.
More preferably still, the glass composition has a redox of less than 0.25% and preferably less than 0.22%. The redox is defined by the ratio of the FeO content to the total iron content, expressed in the form of Fe2O3, the contents being expressed as percentages by weight.
According to an advantageous embodiment of the invention, and in particular for applications of the motor-vehicle side window type, the overall light transmission under illuminant A (TLA) is greater than or equal to 20% and preferably less than 25%.
The grey glasses according to the invention advantageously have a dominant wavelength under illuminant C of between 485 and 495 nm.
Preferably, the glass composition according to the invention has the following colorimetric coordinates under illuminant C in the L*,a*,b* system:
The L*,a*,b* coordinates are defined in the CIELAB system in which L* represents the lightness, a* represents the red-green chromatic component and b* represents the yellow-blue chromatic component.
According to a first variant of the invention, the glass composition has the following colorimetric coordinates under illuminant C:
The colorimetric coordinate B* in this variant may further be between xe2x88x926 to xe2x88x923.
According to a second variant of the invention, corresponding to glass compositions intended for the production of glazing providing enhanced energy protection, the glass composition has the following colorimetric coordinates:
According to a preferred embodiment of the invention, the glass composition comprises the constituents given below within the following weight limits:
With regard to the oxide MgO, according to a first embodiment of the invention, its content is advantageously greater than 2%, in particular for economic reasons.
According to another embodiment, its content is less than 2%; it has been shown that such MgO contents characterize the composition according to the invention by a shift of the maximum of the FeO absorption band to long wavelengths. The limitation of the amount of MgO to 2% and, preferably, its elimination in the glasses of the invention, as intentional addition, make it possible for the infrared absorptivity of the glass to be actually increased. Complete elimination of MgO, which plays an important role in respect of the viscosity, may be at least partly compensated for by an increase in the Na2O and/or SiO2 content.
BaO, which allows the light transmission to be increased, may be added to the compositions according to the invention in contents of less than 4%. This is because BaO has a much weaker effect on the viscosity of the glass than MgO and CaO. Within the context of the invention, the increase in BaO is essentially to the detriment of the alkali metal oxides, of MgO and above all of CaO. Any significant increase in BaO therefore helps to increase the viscosity of the glass, especially at low temperatures. In addition, introducing a high amount of BaO raises the cost of the composition appreciably. When the glasses of the invention contain barium oxide, the amount of this oxide is preferably between 0.5 and 3.5% by weight.
Apart from complying with the abovementioned limits in the case of the variation of the content of each alkaline-earth metal oxide, it is preferable for obtaining the desired transmission properties to limit the sum of the amounts of MgO, CaO and BaO to a value equal to or less than 13%.
When the intention is to produce coloured glasses, the glass compositions may also include one or more colouring agents such as CeO2, TiO2, Cr2O3, V2O5, WO3, La2O3, etc.
The glasses according to the invention may also contain up to 1% of other constituents provided by the impurities of the glass batch materials and/or from the incorporation of cullet into the glass batch and/or coming from the use of refining agents (SO3, Cl, Sb2O3, AS2O3)
To facilitate the melting, and especially to make the latter mechanically beneficial, the matrix advantageously has a temperature corresponding to a viscosity xcex7 such that logxcex7=2, less than 1500xc2x0 C. More preferably still, and especially when producing the substrate from a glass ribbon obtained using the xe2x80x9cfloatxe2x80x9d technique, the matrix has a temperature corresponding to the viscosity xcex7, expressed in poise, such that logxcex7=3.5, T logxcex7=3.5 and a liquidus temperature Tliq which satisfy the relationship:
T(logxcex7=3.5)xe2x88x92Tliq greater than 20xc2x0 C.
and preferably the relationship:
T(logxcex7=3.5)xe2x88x92Tliq greater than 50xc2x0 C.
The invention also concerns a grey glass composition of the soda-lime type having a global light transmission under an illuminant A (TLA) more than 15% for a glass thickness equal to 4.85 mm, said composition comprising colouring agents as follows in the following weight percentage limits: Fe2O3: 0.25-0.65%, preferably 0.3-0.6% and more preferably still 0.3-0.4%; CoO: 150-250 ppm and preferably greater than 185 ppm; NiO: 650-1000 ppm; Se greater than 5 ppm.